This invention relates to a process for the preparation of amino-para-arenediols and to novel intermediates used in their preparation.
Amino-para-arenediols such as 2-amino-1,4-dihydroxybenzene are useful as in the manufacture of fluorescent dyes and as intermediates for making monomers for polybenzoxazoles.
The amino-para-arenediols are typically prepared by reacting a halogenated quinone with ammonia using the conditions described in U.S. Pat. No. 4,337,196 and then subjecting the aminated product to reductive hydrogenation as described in U.S. Pat. No. 4,806,688 to form the desired amino-para-arenediol. Unfortunately this process often yields mixtures of diamino and monoamino isomers which are often difficult to separate.
Attempts to prepare 2-amino-1,4-dihydroxybenzene or similar amino-para-arenediol via a nitration procedure usually results in decomposition of the para-arenediol starting material. For example, the treatment of hydroquinone or 1,4-diacetoxybenzene with white nitric acid results in total decomposition of the starting material. Accordingly, it is not feasible to prepare, by conventional nitration procedures, 2-amino-1,4-dihydroxybenzene and other amino derivatives of dihydric phenols which oxidize in the presence of nitric acid.
What is needed is an economical high yield process which enables the formation of a substantially pure ar-nitro-para-arenediol. Such a process would provide for the efficient production of high purity amino-para-arenediols which could be used as intermediates in the formation of monomers to be employed in making high molecular weight polybenzoxazoles.